1. Field of the Invention
The present invention relates to a vehicle steering device.
2. Description of the Related Art
Japanese Patent Application Publication No, 2004-175122 (JP 2004-175122 A) discloses an electric power steering system (EPS) that includes an electronic control unit (ECU) that includes a function of determining the steering wheel operation state. The ECU described in JP 2004-175122 A computes the product of a time differential value dθh/dt of a steering angle θh detected by a steering angle sensor and torque Tp detected by a torque sensor as a work load W on the steering wheel, and determines the steering wheel operation state using the work load W. Specifically, in the case where the work load W exceeds a predetermined threshold W1 (W1>0) in the positive direction, or in the case where the work load W exceeds a predetermined threshold −W1 in the negative direction, the ECU determines an actual steering state in which a driver is operating the steering wheel.
In the case where the absolute value of the work load W is equal to or less than the threshold W1 and the absolute value of the torque Tp is equal to or less than a predetermined threshold Tp1 (Tp1>0), the ECU determines a state in which the steering wheel is not held. In the case where the absolute value of the work load W is equal to or less than the threshold W1 and the absolute value of the steering angle θh is equal to or less than a predetermined threshold θh1 (θh1>0), the ECU determines a state in which the steering wheel is held.
In the electric power steering system described in JP 2004-175122 A, if an external force (load torque) is input from a road surface when the actual steering wheel operation state indicates that the steering wheel is not held, the torque Tp and the steering angle are varied, which generates the work load W. Therefore, in the related art, it may be erroneously determined that the steering wheel is actually operated even if the steering wheel is not held. In the related art, in addition, the work load W crosses zero when the steering wheel is operated in the opposite direction even if the actual steering wheel steering state indicates that the steering wheel is actually operated. Therefore, it may be erroneously determined that the steering wheel is not held during such a time.